<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <title>Vue Show</title>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/vue/1.0.26/vue.min.js"></script>
    <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.4/css/bootstrap.min.css" />
</head>

<body>
    <div id="app" class="container">
        <form>
            <div v-show="!message">
                <span class="warning">
                You must enter a message
            </span>
            </div>
            <div>
                <textarea v-model="message"></textarea>
            </div>
            <div v-show="message">
                <button type="submit" class="btm">
                Send Message
            </button>
            </div>
        </form>
    </div>
    <script>
        new Vue({
            el:"#app",
            data:{
                message:''
            }
        })
    </script>
</body>

</html>